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Status of the magnet studies in the ARCS (FLUKA)

Status of the magnet studies in the ARCS (FLUKA). E. Bouquerel, A. Mereghetti, V. Vlachoudis & FLUKA Team, CERN (EN-STI-EET) EURO ν , WP4 - Beta Beam Task Meeting 03 rd June 2010, IPHC, Strasbourg. Losses in the Decay Ring.

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Status of the magnet studies in the ARCS (FLUKA)

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  1. Status of the magnet studies in the ARCS (FLUKA) E. Bouquerel, A. Mereghetti, V. Vlachoudis & FLUKA Team, CERN (EN-STI-EET) EUROν, WP4 - Beta Beam Task Meeting 03rd June 2010, IPHC, Strasbourg

  2. Losses in the Decay Ring • -> Aim of the Decay Ring: Store high intensity and high energy beams of β radioactive ions until their decay. • -> 3 main loss sources identified for the Beta-beam: • Losses due to the RF merging • -> occur after the injection and where the momentum acceptance is the lowest • Losses due to collimation • -> occur in the straight section • Losses due to the β-decay of the radioactive ions • -> occur continuously & anywhere within the ring

  3. Losses in the Decay Ring • What we know: • The superconducting magnets are very sensitive to the beam losses: the losses in the superconducting coils must be estimated carefully (quenching issues). • Assumptions: • -> when 1 ion decays, its momentum variation is negligible (Energy taken by the electron and the (anti-)neutrino low compared to the energy of the secondary ion) whereas its charge number increases or decreases by 1 -> Therefore, its magnetic rigidity changes. • -> the secondary ion coming from the decay of 6He2+ (or 18Ne10+) is considered here:

  4. FP6  FP7 updates • Within the FP6, DecayRing dimensions were: -> 994 m long for the arcs -> 2468 m long for each straight section • To optimize the Decay Ring, the solution retained implies (from the previous FP7 meetings) • -> An increase of the magnetic field in the dipoles, 8T (instead of 6T): higherfield in the dipoles. Same kick. • -> Shorterdipoles: 4.28 m (5.7 m). • -> Shorter quadrupoles: 1m (2m) – bigger gradient: 69.5 T/m (45.4 T/m). • -> More compact arcs: 674m (994m) • -> Ratio between long straight section and total length: 40.2% (35.6%) • -> Increase by 12% of the neutrino flux • New Lattice developped (A. Chancé, CEA) • What effects on the power deposited in the magnets of the arcs? • FLUKA …

  5. Design of the Arc in FLUKA • Geometry: • Use of a Python script (A. Mereghetti, CERN/EN-STI-EET): • -> generation of the S-line of the arc from the TWISS file (*.mdx) containing all coordinates and angles of each element located in the decay ring) • -> transcription of the magnetic fields for each dipole/quadrupole; use of Fortran routines. Empty regions where dipoles/quadrupoles stand Geometry + fields checking -> precision of 2nm for a single isotope 6He2+ trajectory circulating through the arc USERDUMP card). x axis (cm) z axis (cm)

  6. Magnets implemented in FLUKA • Empty regions filled with 144 Quadrupoles and 86 SC-Dipoles (replication of prototypes) • Magnets very similar to the ones used for LHC Upgrade: • -> same philosophy • -> same materials • -> different dimensions: lengths/coils quadrupoles Length: 100cm Ext. radius: 28cm Aperture: 16cm Gradient: 70T/m Coil: NbTi

  7. Magnets implemented in FLUKA • Empty regions filled with 144 Quadrupoles and 86 SC-Dipoles (replication of prototypes) • Magnets very similar to the ones used for LHC Upgrade: • -> same philosophy • -> same materials • -> different dimensions: lengths/coils dipoles Length: 425cm Ext. radius: 28cm Aperture: 18cm Field: 8T Coil: NbTi

  8. Power depositions with FLUKA • Simulations performed for 6Li3+ (daughter of 6He2+) on half of the arc • Present studies done using a routine as a source distributing the particles isotropicallyupstream along half of an arc 56.7% of the incoming energy deposited in half of the arc Highest power deposited in the magnets 9.66x1013 particles of 6He2+ accumulated in the Decay Ring* *Eurisol report study, Nov. 2009

  9. Power Depositions & Peaks: first estimations • Decay losses concentrated on the horizontal plane • Normalized to a decay rate in half of the arc: • He: 3.74x1010 decay.s-1 16 14 12 10 8 6 4 2 0 Power deposited (mW/cm3) dipoles z axis (cm) • Max. peak of power deposited in the coils: ~15mW/cm3 for 4 dipoles. • -> Above the quench limit (~4mW/cm3) • Similar peaks when using 1cm thick liner • (stainless steel)

  10. Power Depositions & Peaks: first estimations • Decay losses concentrated on the horizontal plane • Normalized to a decay rate in half of the arc: • He: 3.74x1010 decay.s-1 Power deposited (mW/cm3) quadrupoles z axis (cm) • Max. peak of power deposited in the coils: ~13mW/cm3 for 3 quadrupoles. • -> Above the quench limit (~4mW/cm3)

  11. Simulation Accuracy Sources of errors: • Physics modeling: • Uncertainty in the cross sections • Uncertainty in the modeling used -> Factor ~1.3 on integral quantities like energy deposition (peak included)while for multi differential quantities the uncertainty can be much worse • Layout and geometry assumptions • It is difficult to quantify, experience has shown that a factor of 2 can be a safe limit • Safety factor for the source term: Factor ~1.2 Safety factor to be applied ~2-3

  12. What next? • Use of a decay loss map generated with ACCSIM (F. Jones, A. Chance) (-> kinematics) • Approaches to decrease the peak of the power deposited: • -> Increase the aperture of the magnets? • -> Use of thicker liners? • -> Absorbers?

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